Optical fibers are playing an increasingly important role in communications signal transmission, and are increasingly replacing traditional signal transmission means, such as coaxial cable and twisted pairs. Optical fibers have the advantages of a large signal bandwidth, coupled with relatively small size and light weight. These advantages, however, carry with them certain problems inherent in the nature of the optical fiber cable itself. The optical fibers used in the cables are primarily made of glass or other low ductility materials and are, thus, mechanically fragile, being characterized by a low strain fracture point, especially in tensile loading. As a result, therefore, cable structures have been developed for mechanically protecting the optical fibers in various environments.
One of the structures developed to protect optical fibers has been to include strength members in the cable. The strength members are not involved in signal transmission, but are instead used to limit the strain on the optical fibers and to carry the load of the optical fiber cable where, for example, the cable is suspended above ground.
In. U.S. Pat. No. 4,844,575 of Kinard et al., there is shown a lightweight optical fiber cable which includes a sheath system having two strength members diametrically opposed to one another on each side of a central core formed by a tubular plastic jacket in which the optical fibers are carded. The strength members extend longitudinally along the cable parallel to the axis thereof. The strength members are enclosed in a plastic jacket, and have a predetermined relative tensile and compressive stiffness so that they are capable of withstanding expected compressive and tensile loadings, and are sufficiently coupled with the jacket to provide a composite cable arrangement. The strength members of Kinard et at. are made of a metallic material, such as steel, for example.
In U.S. Pat. No. 5,125,063 of Panuska et at., a lightweight optical fiber cable is shown having at least one bundle of optical fibers disposed within a tubular member forming a cable central core enclosed by a sheath system which includes two elongated longitudinal strength members extending along the length of fiber optical cable. The sheath system also includes a metallic armor layer which encloses a waterblocking tape for providing increased tensile and compressive stiffness, as well as protecting the optical fiber cable from damage.
An inherent problem in the use of metallic strength members, however, arises when exposed optical fiber cable is struck by lightning whereupon the electrical charge may travel along one or both of the strength members which form a part of the cable. Moreover, a lightning strike may also penetrate the cable jacket and strike the metallic sheath of the cable, transmitting electricity along the length of the cable until the electrical current is either dissipated by encountering a ground, or is otherwise shorted out. Also, due to ambient conditions, it is possible that the optical fiber cable may hold a static electrical charge in either the strength elements or the metallic sheath thereof. Grounding of the cable is thus necessary in order to prevent damage to people and property from stray and unexpected electrical current passing through the mechanical components of the optical fiber cable, and to dissipate any static charges.
As a consequence, optical fiber cable is routinely grounded when it is spliced, and where it enters into commercial and residential structures. This is accomplished through the use of conventional bonding and grounding hardware known to those skilled in the art.
In the known bonding and grounding hardware a sealing clamp is passed over the outside of the cable and the plastic cable jacket is then cut and opened to leave a portion of the metallic sheath exposed, as well as the metallic strength members. Thereafter, the metallic strength members are each bent at an angle of approximately 90.degree. from the longitudinal axis of the cable, and the base section of the wire retainer is placed over the cable. The metallic strength members fit within notches formed in the base of the wire retainer, and the sealing clamp is then slid over the base of the wire retainer and tightened to secure the wire retainer to the cable. The excess length of the metallic members protruding beyond the base of the wire retainer are then cut. A bond shoe is then slid between the corrugated metal sheath and the tubular member of the optical fiber cable until the bond shoe stud lies against the end of the metallic sheath, the bond shoe stud being aligned with the wire retainer. Thereafter, a bond plate is placed over the bond shoe, the bond shoe stud being threaded and extending upward therefrom and passed through the bond plate. A second opening in the bond plate is aligned with a corresponding opening formed in the wire retainer so that a threaded fastener can be passed therethrough and into a bonding block which acts to secure the wire retainer, the bond shoe, and the bond plate to the optical fiber cable. Thereafter, a ground wire, or ground wires, provided by a cable installer or splicer, is placed into the bonding block, and secured to the bonding block by set screws to ground the cable.
Although this bonding and grounding hardware known in the art can satisfactorily perform the task of grounding the optical fiber cable, from the foregoing it can be seen that it has a multiplicity of parts and requires a number of steps to install, thus necessitating the expenditure of large amounts of time to assemble the hardware in order to ground the cable properly. Moreover, should the cable installer or splicer misplace or be missing any of the several component parts of this hardware, the cable cannot be successfully grounded, and the dangerous conditions sought to be avoided remain.
What is needed and what seemingly is not available in the art is a universal grounding clip which does not require assembly, or requires only minimal assembly, at the site of its intended use, and which can be quickly and readily fastened to an optical fiber cable in order to ground the metallic strength elements and/or metallic sheath thereof. Desirably, such a grounding clip would be relatively low in cost and have few components or parts.